An image scanning apparatus may have an image recognition device that determines whether a specific image is included in a scanned image or not. Such an image recognition device needs to have a high operation speed and high determination accuracy.
JP-A-9-293082 discloses an image recognition device that lowers resolution of an input image, then calculates a characteristic quantity such as average density, and searches for image data that is stored in advance, in accordance with the characteristic quantity.
However, the determination accuracy is lowered if the operation speed is increased, and the operation speed is lowered if the determination accuracy is increased. Therefore, there is a problem that an image recognition device having a high operation speed and high determination accuracy cannot be provided.
For example, if the operation speed is increased to a certain extent, the determination accuracy is lowered and the slice-out position of an image may be shifted as shown in FIG. 14.
There is also an image recognition device that reduces input image resolution to narrow down a search area and then compares the reduced-resolution image with a high-resolution input image that is stored in advance (see, for example, JP-A-2005-235089).
However, many memories are required in order to store the low-resolution image and the high-resolution image. There also is a problem that it is difficult to carry out signal processing by a hardware circuit such as ASIC since logical conditional branching is necessary when determining the search area narrowed down from the low-resolution image by specifying a high-resolution image area.